Jheni Osman: Trees
In this film Jheni Osman describes how the transport systems in plants, the xylem and phloem, may limit the height to which trees can grow. Transpiration is driven by evaporation from the leaves, pulling water up through the xylem. The taller the tree, the further the water has to move against gravity.
To investigate this scientists climbed giant redwoods and found that the leaves at the top of the trees were in drought, and from this they calculated the maximum height that water could be pulled up through xylem.
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